1. Field of the Invention
The present invention relates to a simplified process for the preparation of a water-soluble vinyl polymer suspension and its use as a thickening agent.
2. Discussion of the Background
Suspensions of water-soluble or water-absorbing vinyl polymers having a high capacity to absorb water are known. These suspensions are typically used as thickeners.
EP 0 297 184 describes ionic resin emulsions having high water absorptivity. The emulsions are prepared by reversed phase emulsion polymerization of an aqueous solution of ionic monomers--in particular (meth)acrylic compounds--with 0.01 to 0.5 mol.% of a divinyl compound, such as methylene bisacrylamide or allyl acrylamide, in the presence of a radical former such as azobisisobutyronitrile.
DE-OS 24 51 599 describes a process to prepare fluid, water-dispersible suspensions comprising dry particles of water-soluble or water-absorbing vinyl polymers in liquid polyglycol or a liquid polyglycol ether. The polymers are prepared individually by polymerization of suitable water-soluble vinyl monomers, such as sodium acrylate, in a water in oil (w/o) emulsion, from which the water is subsequently removed by azeotropic distillation with hydrocarbon oils, such as xylene or halogenated hydrocarbons, at which time the liquid polyglycols or polyglycol ethers are added. Water-absorbing polymers are obtained by polymerization in the presence of crosslinking agents such as methylene bisacrylamide and allyl acrylate.
EP 0 097 808 discloses a water soluble thickener in suspension form. The thickener is a copolymer of an alkali or ammonium salt of acrylic or methacrylic acid with a crosslinking monomer having at least two polymerizable double bonds. The polymer is prepared from an essentially anhydrous solution of monomers in a low aliphatio aloohol, such as ethanol. After the polymer precipitates the alcohol-containing suspension is prepared by mixing with water. The polymer content of these suspensions ranges from 7 to 12% by wt. In example 5 of EP 0 097 808 the polymer content of the suspension is 8% by wt. and the suspension stability achieved was only satisfactory.